如何斯威夫特

Question

顯示圖像爲中心UICollectionViewCell我想表明的，當我在第二項移動居中的圖像爲中心，在UICollectionView第一項顯示圖像，這個項目不居中

let itemsPerRow:CGFloat = 1 
    var sectionInsets = UIEdgeInsets(top: 20.0, left: 20.0, bottom: 20.0, right: 20.0) 
    var productImage = [String]() 


func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int { 
     return productImage.count 
    } 

    func collectionView(_ collectionView: UICollectionView, 
         cellForItemAt indexPath: IndexPath) -> UICollectionViewCell { 
     let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ProductInfoDetailCell", for: indexPath) as! ProductInfoDetailCell 
     cell.productLargeImageView.image = UIImage(named: productImage[indexPath.row]) 
     //cell.productLabel.text = productTitle[indexPath.row] 
     return cell 
    } 




    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize { 

     let paddingSpace = (sectionInsets.left) * (itemsPerRow + 1) 
     let availableWidth = collectionView.frame.size.width - paddingSpace 
     let widthPerItem = availableWidth/itemsPerRow 
     return CGSize(width: widthPerItem , height: 400) 
    } 

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets { 
     return sectionInsets 
    } 

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat { 

     return sectionInsets.left 

    } 

第一圖像，物品是centred-

第二圖像，項不居中

我也使用水平滾動和尋呼UICollectionView

Answer 1

您需要使用自定義UICollectionViewFlowLayout達到你所需要的。

創建的UICollectionViewFlowLayout

class CustomCollectionViewFlowLayout: UICollectionViewFlowLayout 
{ 
    override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint 
    { 
     if let collectionViewBounds = self.collectionView?.bounds 
     { 
      let halfWidthOfVC = collectionViewBounds.size.width * 0.5 
      let proposedContentOffsetCenterX = proposedContentOffset.x + halfWidthOfVC 
      if let attributesForVisibleCells = self.layoutAttributesForElements(in: collectionViewBounds) 
      { 
       var candidateAttribute : UICollectionViewLayoutAttributes? 
       for attributes in attributesForVisibleCells 
       { 
        let candAttr : UICollectionViewLayoutAttributes? = candidateAttribute 
        if candAttr != nil 
        { 
         let a = attributes.center.x - proposedContentOffsetCenterX 
         let b = candAttr!.center.x - proposedContentOffsetCenterX 
         if fabs(a) < fabs(b) 
         { 
          candidateAttribute = attributes 
         } 
        } 
        else 
        { 
         candidateAttribute = attributes 
         continue 
        } 
       } 

       if candidateAttribute != nil 
       { 
        return CGPoint(x: candidateAttribute!.center.x - halfWidthOfVC, y: proposedContentOffset.y); 
       } 
      } 
     } 
     return CGPoint.zero 
    } 
} 

2.一個子類中storyboard的Collection View Flow Layout類爲CustomCollectionViewFlowLayout。